I suspect that DVDA has determined to recompress your input file. At a minimum, the audio you listed is non-compliant for DVD, so it will need to be recompressed in DVDA4.
In DVDA4, go File/Optimize DVD -- then check under the VIDEO1 and AUDIO1 tabs to see if recompress is required...
Anytime DVDA has to deal with possibly recompressing things, it gives strange indications about space requirements. This has been the case since 1.0 of the product, and while I think work has been done to improve things, there are still a few kinks.
That's why I asked about you A/V file sizes - if the files you are feeding in to DVDA are small enough to fit on a DVD, then you usually don't need to worry about DVDA's size estimates. Though if the size is off, it's usually a good indicator that you did something wrong and that DVDA may end up doing something you don't want (such as recompressing the video stream).